Catalytic process of preparing unsaturated acids and aldehydes



United States Patent 3,401,196 CATALYTIC PROCESS OF PREPARING UNSATU-RATED ACIDS AND ALDEHYDES Jamal S. Eden, Akron, Ohio, assignor to The B.F. Goodrich Company, New York, N.Y., a corporation of New York NoDrawing. Filed Aug. 30, 1965, Ser. No. 483,801

8 Claims. (Cl. 260533) This invention relates to new and usefulcatalysts and to a method of preparing unsaturated aldehydes andunsaturated carboxylic acids by oxidation of unsaturated hydrocarbons atan elevated temperature, and relates more particularly to catalystscomprising a mixture of a molybdenum oxide, tellurium oxide and anuranium phosphate in a molar ratio of 100 M00 -100 TeO and 10-100 of auranium phosphate and to a method of preparing acrolein and acrylicacid, or methacrolein and methacrylic acid by passing vapors ofpropylene or isobutylene and an oxygen containing gas over the catalystat a temperature of from about 325 C. to about 550 C. The catalyst canalso be designated as with the P being in the form of a phosphate i.e.each P is attached to 3 or 4 oxygen atoms.

Numerous attempts have been made in the past to prepare products ofhigher oxidation state from hydrocarbons, especially from the normallygaseous hydrocarbons. However, all prior catalysts and procedures foroxidizing monoolefinic gaseous hydrocarbons to monoolefinicallyunsaturated aldehydes or monoolefinically unsaturated carboxylic acidswith the same number of carbon atoms as the hydrocarbon having seriousshortcomings. The catalysts either have a very short active life, orthey convert only a portion of the hydrocarbon to desired end groups perpass; they oxidize the hydrocarbon excessively to form high proportionsof carbon monoxide or carbon dioxide or both; they 'are notsuflficiently selective, so that the hydrocarbon molecule is attacked atboth the olefinic unsaturation and at a methyl group; or the oxidationof the olefin does not proceed beyond the aldehyde stage.

It is therefore uexpected to find 'a catalyst having unusually long lifethat will convert a substantial amount, more than 50% per pass, of agaseous monoolefin such as propylene or isobutylene to yield very highproportions of acrolein and acrylic acid, or methacrolein 'andmethacrylic acid. It is also unexpected to find a catalyst that producesa wide ratio of olefinic aldehyde to monoolefinically unsaturatedcarboxylic acid by controllable changes in reaction conditions orcatalyst composition. Mol percent efficiencies of about 60 for thealdehyde and about for the unsaturated carboxylic acid have beenobtained with the catalyst and process of this invention. Usually whenthe efficiency for conversion of the hydrocarbon to aldehyde is high theefiiciency for the conversion to acid is low and vice versa. Thisprovides a degree of flexibility in the process, so as to provide meansfor obtaining a product mix that is needed at any particular time duringcommercial operation.

The reactants The essential reactants are (l) propylene or isobutyleneand (2) 'an oxygen containing gas, which can be pure oxygen, oxygendiluted with an inert gas, oxygen enriched air or air without additionaloxygen. For reasons of economy, air is the preferred oxygen containingreactant.

For the purpose of this invention the hydrocarbons 3,401,196 PatentedSept. 10, 1968 which are oxidized can be defined generically by theformula wherein it is also apparent that the end products formed resultfrom the oxidation of only one methyl group on the hydrocarbon moleculewhile the terminal CH =C remains intact.

Stoichiometric ratios of oxygen to olefin for the purpose of thisinvention are 1.5 to 1. Slightly lower amounts of oxygen can be used ata sacrifice of yield. It is preferred, however, to use 33 to 66% excessoxygen. Larger excesses do not impair the yields of aldehydes and acids,but for practical considerations an excess much above 100% would requireextremely large equipment for a given production capacity.

The addition of steam into the reactor along with the hydrocarbon andoxygen containing gas is desirable but not absolutely essential. Thefunction of steam is not clear, but it seems to reduce the amount ofcarbon monoxide and dioxide in the efiluent gases.

Other diluent gases can be used. Surprisingly, saturated hydrocarbonssuch as propane are rather inert under the reaction conditions.Nitrogen, argon, krypton or other known inert gases can be used asdiluents if desired but are not preferred because of the added cost.

The catalyst and its preparation There are several methods for thepreparation of the catalyst, which can be supported or unsupported. Itis possible to dissolve each of the starting ingredients in Water andcombine them from the aqueous solutions or the ingredients can be dryblended. Because of the more uniform blend obtained by the solutionprocedure, it is preferred.

The general procedure for preparing a catalyst from water solubleingredients is to dissolve the requisite amounts of a molybdenum salt, atellurium salt and an uranium salt in water. Add the requisite amount ofphosphoric acid to the uranium salt solution. Add the telluriurn saltsolution to the molybdenum salt solution and then add the uraniumsalt-phosphoric acid mixture to the molybdenum-tellurium salt mixture.The catalyst is then dried and baked at 400 C. for about 16 hours.

Supported catalysts can be prepared by adding a dry support or anaqueous slurry thereof to the aqueous solution of catalyst or theaqueous catalyst ingredients can be added to the slurry of the support.

Alternatively a slurry of the catalyst ingredients can be prepared inwater, then dried and baked. For supported catalysts the aqueous slurryof the catalyst ingredients can be added to an aqueous suspension of thesupport or vice versa, and then dried and baked.

Another method is to blend the dry ingredients of the desired particlesize and then mix them thoroughly. Thorough blending and uniformparticle size is desired.

A specific example of the solution method is now set forth.

(1) Add 50.9 g. of molybdic acid to 100 grams of an aqueous colloidaldispersion of microspheroidal silica in a concentration of 30-35% 'SiO(Ludox H.S.).

(2) 15.96 g. of TeO is added to (l).

(3) Dissolve 40.18 g. of (UO (NO -6H O in water and add 9.24 g. of H POAdd this mixture slowly to the mixture of (l) and (2).

Dry on a steam bath and bake for 16 hours at 400 C. Thereafter, thecatalyst is ground to the desired mesh size and sieved.

Among the suitable supports are silica, silica containing materials,such as diatomaceous earth, kieselguhr, silicon carbide, clay, aluminumoxides and even carbon, although the latter tends to be consumed duringthe reaction.

The exact chemical structure of the catalysts made by the aboveprocedures is not known, but catalysts with molar ratios of 100 Mo,10l00 Te and 10100 of a uranyl phosphate can be used for oxidizing themonoolefinic hydrocarbon to aldehyde and/ or carboxylic acid. Thecatalyst contains chemically bound oxygen so that the generic formulacan be written as or other uranyl phosphate 10400. The phosphate can bea P radical, a pyrophosphate, or a polyphosphate.

Reaction conditions The reaction can be carried out in either a fixed orfluidized catalyst bed.

The reaction temperature can range from about 300 to 450 C. for theoxidation of propylene but the preferred range is from about 350 toabout 425 C. Below 350 C. the conversion per pass is lower and lowtemperature tends to produce more aldehyde than desired. Usually, alonger contact time is needed at lower temperatures to obtain the yieldsof desired products obtainable at higher temperatures. Above 425 C. inthe propylene oxidation some of the desired end products appear to beoxidized to carbon oxides. This is much more apparent at 450 C. Forisobutylene, oxidation temperatures of 375-550 are desirable with thepreferred range being 300450 C.

The molar ratio of oxygen to propylene or isobutylene should be at least2 to 1 for good conversion and yields. Some excess oxygen, 33 to 66 molpercent is even more desirable and is preferred. There is no criticalupper limit as to the amount of oxygen, but when air is used as theoxygen containing gas it becomes apparent that too great an excess willrequire large reactors, pumping, compressing and other auxiliaryequipment for any given amount of desired end product. It is thereforebest to limit the amount of air to provide a 33 to 66% excess of oxygen.This range provides the largest proportion of acid, under given reactionconditions. Also, since care is needed to avoid an explosive mixture,the limiting of air aids in that direction.

The molar ratio of steam to propylene or isobutylene can range from 0 toabout to 7, but best results are obtained with molar ratios of about 3to 5 per mol of olefin and for this reason are preferred.

The contact time can vary considerably in the range of about 2 to 70seconds. Best results are obtained in a range of about 8 to 54 secondsand this range is preferred. Longer contact times usually favor theproduction of acid at any given temperature.

The particle size of catalyst for fixed bed operations used is from10-18 mesh. As is known, for fixed beds, the size may be of a widerrange particle size. For fluid bed systems the catalyst size should befrom 80-325 mesh (U.S. Sieve).

The reaction can be run at atmospheric pressure, in a partial vacuum orunder induced pressure up to 5 O-100 p.s.i. Atmospheric pressure ispreferred for fixed bed systems and a pressure of 1 to 100 p.s.i. forfluid bed reactions. Operation at a pressure which is below the dewpoint of the unsaturated acid at the reaction temperature isadvantageous.

The data in the examples show that wide variations in percentages ofunsaturated acids and aldehydes can be obtained with a single catalyst,using fixed ratio of reactants but changing the temperature and/orcontact time. Further variation is obtainable by controlling the othervariables in the reaction including the catalyst compositions within thelimits set forth herein.

The examples are intended to illustrate the invention but not to limitit.

The examples A series of runs was made in a fixed bed reactor of a highsilica (Vycor) glass tube 12 inches long and 30 mm. outer diameter. Thereactor had three inlets, one for air, one for steam and one forpropylene. Three external electrically operated heating coils were woundon the reactor. One of the coils extended along the entire length of thereactor and each of the remaining coils extended only about one half thelength of the reactor.

Outlet vapors were passed through a short water cooled condenser.Uncondensed gases were passed through a gas chromatograph (Perkin-Elmermodel 154D) and analyzed continuously. The liquid condensate was weighedand then analyzed for acrylic acid and acrolein in the gaschromatograph.

The reactor was filled to about of its capacity with 170 ml. of acatalyst made by the solution method described above, using a ratio of75 M00 25 TeO and 10 (UO P O Empirically the catalyst is and the P ispresent as P O The catalyst was not supported and had a mesh size of10-18 (U.S. Sieve).

Steam at a temperature of ZOO-250 C. was first passed into the reactor.Then propylene and air were separately fed into the stream of watervapor. This mixture then passed through a pre-heater and entered thereactor at about ZOO-250 C. The reactor was pre-heated to about 285 C.before the gas feed was begun.

The ratio of reactants was about 2.955 mols of oxygen and 4.25 mols ofsteam per mol of propylene. Cold contact time was 20.4 seconds.

The reaction temperature was varied as the reaction proceeded.

The table below summarizes the data obtained in these runs:

Mel Mel percent yield on M01 percent efliciency filun Temp., percent:propylene converted C. proplylene converted Aer. AA Aer. AA

Aer. Acrolcin. AA=Acry1ic acid.

I claim:

1. A method of preparing a mixture of unsubstituted monoolefinicaldehydes and monoolefinic monocarboxylic acids by oxidation of a methylgroup of a hydrocarbon having the structure in which each P is combinedwith 3 to 4 atoms of oxygen, and the U0 to P ratio ranges from 3UO to 2?to 5UO to GP.

2. A method of preparing a mixture of acrolein and acrylic acidcomprising passing a mixture of propylene, and an oxygen containing gascontaining from about 1.5 to 4 mols of oxygen per mol of propylenethrough a bed of a catalyst having the empirical formula in which each Patom is combined with 3 to 4 atoms of oxygen and the U0 to P ratioranges from 3UO to 2P to SUO to 6P, at a temperature of from about 350C. to about 450 C.

3. The method of claim 2 in which the U0 to P ratio is l.

4. The method of claim 2 in which the catalyst has the empirical formulaMO1OQTC33 33UO225 65P26 66O436 5 and the P is present as P O 5. Themethod of claim 2 wherein the catalyst contains, in molar ratios, 100M00 10-100 TeO and 10-100 2)2 2 7- 6. A method of preparing a mixture ofacrylic acid comprising passing a mixture of propylene, an oxygen 10containing gas containing from about 1.5 mols of oxygen per mol ofpropylene and up to 7 mols of water vapor per mol of propylene through abed of a catalyst comprising Mo Tc UO P- 0 in the P is present as P O ata temperature of from about 360 to about 425 C.

7. A method of preparing a mixture of methacrolein and methacrylic acidcomprising passing a mixture of isobutylene and an oxygen containing gasin an amount suflicient to provide from about 1.5 to about 3 mols ofoxygen per mol of isobutylene, through a bed of a catalyst comprising MOoTe1 10UO 2o)P2 2oO39 120 in the 6 U0 to P ratio ranges from 3:2 to 5:6,and in which each P is combined with 3 to 4 atoms of oxygen.

8. The method of claim 6 in which the catalyst is MO o Te UN 2 5P2 5O4in which the P is present as a phosphate.

References Cited UNITED STATES PATENTS 3,065,264 11/1962 Koch et a1.260-533 3,192,259 6/1965 Fetterly et a1. 260-533 FOREIGN PATENTS 839,8086/ 1960 Great Britain. 903,034 8/ 1962 Great Britain.

OTHER REFERENCES HENRY R. JILES, Primary Examiner.

0 D. E. STENZEL, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,401,196 September 10 1968 Jamal S. Eden It is certified that error appearsin the above identified patent and that said Letters Patent are hereb;corrected as shown below:

Column 4, line 70, the formula should appear as shown below:

Column 6, line 4, the formula should appear as shown below:

Signed and sealed this 9th day of June 1970.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR.

1. A METHOD OF PREPARING A MIXTURE OF UNSUBSTITUTED MONOOLEFINICALDEHYDES AND MONOOLEFINIC MONOCARBOXYLIC ACIDS BY OXIDATION OF A METHYLGROUP OF A HYDROCARBON HAVING THE STRUCTURE